fix model name

Author: crashmovies

.github/workflows/presubmit.yml

@@ -32,4 +32,4 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           LLM_API_KEY: ${{ secrets.LLM_API_KEY }}
-          LLM_MODEL: "gemini-1.5-flash"
+          LLM_MODEL: "gemini-2.5-flash-preview-09-2025"